In the treatment of heart malfunctions, cutting, or ablation, of specific conduction paths in the region of the A-V node, the His bundle, or the ventricles has been found beneficial. This can be accomplished surgically, but recently more preferable, nonsurgical techniques have been developed.
In one prior art technique, a catheter having an optical fiber passing through it is advanced to the desired location in the heart. Energy from an external laser is conducted by the optical fiber into the heart. This technique is described by Onkar S. Narula et al in "Microtransection of the His Bundle With Laser Radiation Through a Pervenous Catheter: Correlation of Histologic and Electrophysiologic Data," Am. J. Cardiology, July, 1984, pp. 186-192. The equipment necessary for laser ablation is relatively expensive, and the optical fiber is somewhat difficult to maneuver to the desired location.
A technique for high frequency ablation of the His bundle in the heart is disclosed in U.S. Pat. No. 4,641,649 issued Feb. 10, 1987 to Walinsky et al. A catheter in the form of a coaxial transmission line with an antenna at its distal end is advanced into the heart in the region of the His bundle, and the potentials sensed by the catheter are measured and displayed. The catheter position is adjusted until the desired potentials are obtained. Then, high frequency energy is applied to the transmission line, causing ablation of portions of the His bundle. The high frequency technique may produce undesirable charring of tissue surrounding the antenna.
In an electroshock ablation technique, a catheter provided with one or more electrodes is advanced through a blood vessel into the heart, and a plate-like electrode is positioned on the patient's skin. A high energy electrical pulse is applied between the electrodes, causing a modification of the conduction system by ablation. Such a technique is described by J. Gallagher et al in "Catheter Technique for Closed Chest Ablation of the Atrioventricular Conduction System," N. E. J. Medicine, Vol. 306, No. 4, Jan. 28, 1982, pp. 194-200 and by Melvin M. Scheinman et al in Catheter-Induced Ablation of the Atrioventricular Junction to Control Refractory Supraventricular Arrhythmias," JAMA, Vol. 248, No. 7, Aug. 20, 1982, pp. 851-855. A voltage on the order of 2,000 volts is applied for a time on the order of a few milliseconds.
One problem associated with prior practice of the electroshock ablation technique has been that arcing often occurs in the region of the electrode. Such arcing can cause undesired burning of tissue and produces shock waves which can further damage the surrounding tissue. The arcing occurs across bubbles which form at the surface of the electrode when it is energized. It is desirable to minimize arcing and the resulting shock waves.
In the past, electroshock ablation has been performed with conventional pacing catheters which include ring electrodes and distal electrodes that are similar to ring electrodes but have a rounded tip. When these electrodes are used for electroshock ablation, arcing often occurs. A variety of other electrode shapes have been disclosed for pacing applications. In pacing applications, the applied voltage is on the order of a few volts, and arcing is not a factor.
PCT Publication No. WO 80/02231 published Oct. 30, 1980, relates to an electrode lead for pacemakers wherein a conductive electrode tip has a spherical portion and a cylindrical portion attached to the distal end of the catheter. The cylindrical portion is tapered to a smaller diameter at the intersection with the spherical portion. The cylindrical portion is not insulated.
U.S. Pat. No. 3,757,789 issued Sept. 11, 1973 to Shanker relates to an electrode for use in a body organ stimulator such as a cardiac pacer. The electrode system includes a spherical electrode tip with electrical connection made by a cylindrical pin of smaller diameter than the sphere. The catheter tube is tapered to a smaller diameter at the intersection with the spherical electrode tip.
U.S. Pat. No. 1,932,258 issued Oct. 24, 1933 to Wappler discloses a surgical electrode for transmission of high frequency electrical energy to body tissue. The electrode includes a flat, blade-like arm which produces a cutting spark when brought into contact with tissue and a spherical arm which is used for coagulation in a nonsparking manner.
U.S. Pat. No. 4,660,571 issued Apr. 28, 1987 to Hess et al discloses a percutaneous lead with a hemispherical distal electrode and a ring electrode. The lead is suitable for use in mapping, ablation and pacing.
It is a general object of the present invention to provide improved apparatus for nonsurgical electroshock ablation of desired portions of internal body organs.
It is another object of the present invention to provide improved apparatus for electroshock ablation of tissue within the heart.
It is a further object of the present invention to provide an electroshock ablation catheter with a contoured electrode that provides a high arcing threshold.
It is yet another object of the present invention to provide an electroshock ablation catheter having at or near its distal end a contoured electrode that permits application of high voltage, high current pulses to tissue without arcing.